Sen. Chuck Grassley has called for a federal probe into the country’s largest chain of psychiatric hospitals after BuzzFeed News published videos showing employees of one of its Alabama facilities beating and dragging young patients.

The story was part of a two-year investigation into Universal Health Services, or UHS, which owns more than 200 mental health facilities across the country that made more than $8 billion in revenue last year.

“The continued reporting on UHS facilities shows a disturbing trend of behavior,” Grassley wrote in a letter to the inspector general of the Department of Health and Human Services last week. ”The most recent allegations cause significant concern about whether UHS has the ability to adequately manage the facilities under its control.”

The article, based on interviews, documents, and surveillance videos, found that staff members at Hill Crest Behavioral Health in Birmingham sometimes assaulted young patients or placed them in dangerous chokeholds instead of performing proper physical restraints. Staff members and patients also said the facility administered medications as a means of control. Other employees said they were instructed to falsify medical records.

“These are serious allegations and the continuing reports further show an alarming pattern of conduct surrounding UHS facilities and its apparent inability to adequately manage its staff,” Grassley, a Republican from Iowa, wrote.

He called on the federal agency to “explain what steps your office is taking to investigate UHS for the aforementioned abuses at Hill Crest Behavioral Health.”

Hill Crest has previously stated that it regrets the instances of inappropriate conduct by its staff. It added that the surveillance videos showed “isolated incidents” that are “not indicative of the quality of care provided at Hill Crest.”

This is the third time that the senator has written to the inspector general of the Department of Health and Human Services about UHS. He first wrote to the department last December after BuzzFeed News revealed that employees at 10 UHS facilities across nine states said they were under pressure to fill beds by almost any means, including twisting people’s words to make them seem suicidal. He wrote to the department again in April following a BuzzFeed News report on one of the company’s facilities in Oklahoma where riots and understaffing endangered both patients and employees alike.